Molybdenum doped induced amorphous phase in cobalt acid nickel for supercapacitor and oxygen evolution reaction

Water oxidation on a sustainable polymeric proton relay: the role of post-phosphating of an oxide sub-layer on PCET

Lagging proton transfer (PT) toward electron transfer (ET) during multi-step proton-coupled electron transfer (PCET) is one of the humble approaches toward complete biomimicking of artificial leaves. In this work, we synthesized a typical sustainable polymeric interface (poly L-lysine) to investigate the effect of post-phosphating of the metal oxide substrate (NF/CoMoO4) on the yield of PCET during the electrocatalytic water oxidation reaction (WOR) in alkaline medium. The details of the PCET mechanism are unraveled using the kinetic isotope effect (KIE), proton inventory, Tafel slopes, pH studies, and high-frequency transmission line (Gerischer) impedance. The appealing Gerischer feature unveils an electrochemical reaction preceded and followed by a chemical exchange reaction (CEC mechanism), indicating a proton hopping mechanism that practically blocks natural diffusion of the protonic species (H+ and H2O) and the role of the interfacial phosphate#p-Lys hydrogen bond network (HBN) in PCET. The interfacial HBN can serve as a flexible proton hook to delocalize protons and may polarize the O-O bond, thereby facilitating the overall PCET for the progress of O-O bond formation. Poly L-lysine improved the response stability of the PCET catalyst through corrosion protection of the metallic substrate and also prevention of the spatiotemporal accumulation of protons as a surface corrosion agent. The results show a non-concerted PCET mechanism with the first ET step as the RDS of the heterogeneous WOR.

Synergistic regulation of d-band center photocatalytic hydrogen evolution at S-scheme heterojunction reduction sites through defect engineering and interface electric field

The efficiency of photocatalytic hydrogen evolution can be significantly enhanced while maintaining cost-effectiveness through the synergistic effect of defect surface engineering and multi-component heterojunctions. The structure and properties of NiCo2O4 nanorods were modified by inducing oxygen vacancies at different temperatures in this study, resulting in improved optical properties and electron adsorption capacity. The presence of oxygen vacancies leads to a reduction in the band gap of NiCo2O4, thereby enhancing electron transport efficiency through band gap engineering. Simultaneously, surface properties undergo changes, and vacancy defects serve as electron trapping centers, facilitating an increased participation of electrons in the hydrogen evolution reaction process. The dodecahedron KMP with a cavity structure is additionally introduced to form an S-scheme heterojunction with NiCo2O4. This establishes a novel mechanism for electron transport, which effectively enhances the separation of electron-hole pairs and improves the redox capacity of the photocatalytic system. The adsorption of intermediates in the hydrogen production process is enhanced through synergistic regulation of d-band centers via surface defect engineering and S-scheme heterojunction. Additionally, this approach improves the separation efficiency of electron-hole pairs and accelerates electron transfer dynamics, significantly enhancing hydrogen production efficiency.

Synergistic effects of interface and phase engineering on telluride toward alkaline/neutral hydrogen evolution reaction in freshwater/seawater

The development of efficient, stable, and versatile hydrogen evolution electrocatalysts is of great meaning, but still faces challenging. Interface engineering and phase engineering have been immensely applied in the field of hydrogen evolution reaction (HER) because of their unique physicochemical properties. However, they are typically used separately, which limits their effectiveness. Herein, we propose an interface-engineered CoMo/CoTe electrocatalyst, consisting of an amorphous CoMo (a-CoMo) layer-encapsulated crystalline CoTe array, achieving the profound optimization of catalytic performance. The experimental results and density functional theory calculations show that the d-band center of the catalyst shifts further upward in contrast with its crystalline-crystalline counterpart, optimizing the electronic structure and the intermediate adsorption, thereby reducing the kinetic barrier of HER. The a-CoMo/CoTe with superhydrophilic/superaerophobic features shows excellent catalytic performance in alkaline, neutral, and simulated seawater environments.

Electrodeposition synthesis of cobalt-molybdenum bimetallic phosphide on nickel foam for efficient water splitting

A reasonable design of excellent bifunctional catalyst is an effective strategy for large-scale hydrogen production. In this study, a two-stage electrodeposition method was used to prepare a crystalline-amorphous structure cobalt molybdenum phosphide layered particles with different sizes on a nickel foam (NF) substrate. Electron rearrangement at the Co/CoMoP2@CoMoO4 heterogeneous interface can reduce the reaction energy barrier for HER and OER, and accelerate the catalytic reaction kinetics. The doping of Mo can promote the synergistic effect between Co and Mo, thereby optimizing the Gibbs free energy of hydrogen adsorption/desorption. This layered arrangement of different size particles greatly improves the active area of the catalyst. In alkaline solution, achieving a current density of 10 mA cm-2 only required overpotentials of 40 mV for HER and 278 mV for OER, respectively. The cell voltage required for the CoMo-P/NF||CoMo-P/NF electrolytic cell is only 1.53 V at 10 mA cm-2. This study provides a reference for the rapid, efficient, and environmentally friendly preparation of high-activity water splitting catalysts with large surface areas.

Opposite Electron Transfer Induced High Valence Mo Sites for Boosting the Water Splitting Performance of Ir Atoms

Developing highly efficient and low-cost bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting poses significant challenges. In this study, a novel bifunctional electrocatalyst, Irn-CoMoPOx, was achieved via incorporating low-loading Ir single atoms and clusters with the high-valence Mo6+ modified CoPOx nanosheets. The Irn-CoMoPOx catalyst demonstrates remarkable low overpotentials of 222 mV and 36 mV for the OER and HER, respectively, in delivering a current density of 10 mA cm-2. When employed as both the anode and cathode catalyst in overall water splitting, the Irn-CoMoPOx∥Irn-CoMoPOx configuration exhibits a superior cell voltage of 1.53 V, outperforming the benchmark Pt/C∥IrO2 electrolytic cell (1.60 V) for achieving the current density of 10 mA cm-2. Benefiting from the high-valence of Mo species, the metal-support interaction of Irn-CoMoPOx was greatly strengthened, resulting in an order of magnitude increase in the mass activity of Ir for the HER. The high valence of non-noble metals plays a crucial role in tuning the local electronic configurations and optimizing the adsorption energies of the intermediates, which synergistically improves the overall performance of Ir in water splitting. The study provides valuable insights for future research in the utilization of Ir-based bifunctional catalysts for overall water electrocatalysis applications.

Enhancing supercapacitor performance of Ni-Co-Mn metal-organic frameworks by compositing it with polyaniline and reduced graphene oxide

Metal-organic frameworks (MOFs) are one of the most sought-after materials in the domain of supercapacitors and can be tailored to accommodate diverse compositions, making them amenable to facile functionalization. However, their intrinsic specific capacitance as well as energy density is minimal, which hinders their usage for advanced energy storage applications. Therefore, herein, we have prepared six electrodes, i.e., Ni-Co-Mn MOFs, polyaniline (PANI), and reduced graphene oxide (rGO) along with their novel nanocomposites, i.e., C1, C2, and C3, comprising MOFs : PANI : rGO in a mass ratio of 100 : 1 : 0.5, 100 : 1 : 1, and 100 : 1 : 10, respectively. The polyaniline conducting polymer and rGO enabled efficient electron transport, enhanced charge storage processes, substantial surface area facilitating higher loading of active materials, promoting electrochemical reactions, and ultimately enhanced nanocomposite system performance. As a result, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques confirmed the successful synthesis and revealed distinct morphological features of the materials. Following electrochemical testing, it was observed that composition C2 exhibited the highest performance, demonstrating a groundbreaking specific capacitance of 1007 F g-1 at 1 A g-1. The device showed a good energy density of 25.11 W h kg-1 and a power density of 860 W kg-1. Remarkably, the device demonstrated a capacity retention of 115% after 1500 cycles, which is a clear indication of the wettability factor, according to the literature. The power law indicated b-values in a range of 0.58-0.64, verifying the hybrid-type behavior of supercapacitors.

Design strategy for high-performance bifunctional electrode materials with heterogeneous structures formed by hydrothermal sulfur etching

The synthesis of efficient, stable, and green multifunctional electrode materials is a long-standing challenge for modern society in the field of energy storage and conversion. To this end, we successfully synthesized five bimetallic precursor materials with excellent performance by hydrothermal reaction with the assistance of a high concentration of polyvinylpyrrolidone (PVP), and then, sulfide etched the lamellar precursor materials among them to obtain the one-dimensional heterostructured samples. Benefiting from the synergistic effect of the bimetal and the continuous electron/ion transport structure, the samples displayed excellent bifunctional activity in supercapacitor and oxygen evolution reaction (OER). Regarding supercapacitors, the exceptional performance of 2817.2 F g^-1 at 1 A g^-1 was demonstrated, while the asymmetric supercapacitors made showed an extraordinary energy density of 150.2 Wh kg^-1 at a power density of 618.5 W kg^-1 and outstanding cycling performance (94.74% capacity retention after 20,000 cycles at 10 A g^-1). Simultaneously, a wearable flexible electrode that can be wrapped around a finger was coated on a carbon cloth and was found to light up a 0.5-m-long strip of light. Moreover, it exhibited an ultralow oxygen reduction overpotential of 249 mV at 10 mA cm^-2. Hence, our work provides a facile strategy to modulate the synthesis of heterogeneous structured sulfides with a continuous electron/ion transport pathway, which possesses excellent oxygen reduction electrocatalytic performance while meeting superior supercapacitor performance. Such work provides an effective approach for the construction of multifunctional electrochemical energy materials.

Synthesis of active-site rich molybdenum-doped manganese tungstate nanocubes for effective electrochemical sensing of the antiviral drug (COVID-19) nitazoxanide

Nitazoxanide (NTZ), a promising antiviral agent, is currently being tested in clinical trials as a potential treatment for novel coronavirus disease 2019 (COVID -19). This paper describes a one-pot hydrothermal synthesis to prepare molybdenum (Mo)-doped manganese tungstate nanocubes (Mo-MnWO4 NCs) for the electrochemical sensing of NTZ. The as-prepared Mo-MnWO4 NCs were characterized using various techniques such as XRD, Raman, FE-SEM, FE-TEM, and XPS to confirm the crystal structure, morphology, and elemental composition. The obtained results demonstrate that Mo doping on MnWO4 generates many vacancy sites, exhibiting remarkable electrochemical activity. The kinetic parameters of the electrode modified with Mo-MnWO4 NCs were calculated to be (Ks) 1.1 × 10-2 cm2 s-1 and (α) 0.97, respectively. Moreover, a novel electrochemical sensor using Mo-MnWO4 NCs was fabricated to detect NTZ, which is used as a primary antibiotic to control COVID-19. Under optimal conditions, the electrochemical reduction of NTZ was determined with a low detection limit of 3.7 nM for a linear range of 0.014-170.2 μM with a high sensitivity of 0.78 μA μM-1 cm-2 and negligible interference with other nitro group-containing drugs, cations, and anions. The electrochemical sensor was successfully used to detect NTZ in the blood serum and urine samples and achieved high recoveries in the range of 94-99.2% and 95.3-99.6%, respectively. This work opens a way to develop high-performance sensing materials by exploring the introduction of defect engineering on metal tungstates to detect drug molecules for practical applications.

Design of Ni(OH)2 Nanosheets@NiMoO4 Nanofibers' Hierarchical Structure for Asymmetric Supercapacitors

Transition-metal-based materials show great promise for energy conversion and storage due to their excellent chemical properties, low cost, and excellent natural properties. In this paper, through simple strategies such as classical electrospinning, air calcination, and the one-step hydrothermal method, a large area of Ni(OH)₂ nanosheets were grown on NiMoO₄ nanofibers, forming NiMoO₄@Ni(OH)₂ nanofibers. The one-dimensional nanostructure was distributed with loose nanosheets, and this beneficial morphology made charge-transfer and diffusion more rapid, so the newly developed material showed good capacitance and conductivity. Under the most suitable experimental conditions, the optimal electrode exhibited the highest specific capacitance (1293 F/g at 1 A/g) and considerable rate capability (56.8% at 10 A/g) under typical test conditions. Most interestingly, the corresponding asymmetrical capacitors exhibited excellent electrochemical cycle stability, maintaining 77% of the original capacitance. NiMoO₄@Ni(OH)₂ nanofibers were verified to be simple to prepare and to have good performances as energy-storage devices within this experiment.

Effect of Hydrothermal Method Temperature on the Spherical Flowerlike Nanostructures NiCo(OH)4-NiO

NiCo(OH)4-NiO composite electrode materials were prepared using hydrothermal deposition and electrophoretic deposition. NiCo(OH)4 is spherical and flowerlike, composed of nanosheets, and NiO is deposited on the surface of NiCo(OH)4 in the form of nanorods. NiCo(OH)4 has a large specific surface area and can provide more active sites. Synergistic action with NiO deposits on the surface can provide a higher specific capacitance. In order to study the influence of hydrothermal reaction temperature on the properties of NiCo(OH)4, the prepared materials of NiCo(OH)4-NiO, the hydrothermal reaction temperatures of 70 °C, 90 °C, 100 °C, and 110 °C were used for comparison. The results showed that the NiCo(OH)4-NiO-90 specific capacitance of the prepared electrode material at its maximum when the hydrothermal reaction temperature is 90 °C. The specific capacitance of the NiCo(OH)4-NiO-90 reaches 2129 F g−1 at the current density of 1 A g−1 and remains 84% after 1000 charge–discharge cycles.

TEA driven C, N co-doped superfine Fe3O4 nanoparticles for efficient trifunctional electrode materials

Poor conductivity is an obstacle that restricts the development of the electrochemistry performance of Fe₃O₄. In this work, a novel carbon and nitrogen co-doped ultrafine Fe₃O₄ nanoparticles (CN-Fe₃O₄) have been synthesized by triethylamine (TEA) induction and subsequent calcination. The addition of TEA could not only regulate the size of Fe₃O₄ nanoparticles, but also promote the formation of amorphous carbon layer. Well-designed CN-Fe₃O₄ heterostructures provide a highly interconnected porous conductive network, large heterogeneous interface area, large specific surface area and a large number of active sites, which greatly improve conductivity and promote electron transfer and electrolyte diffusion. The prepared CN-Fe₃O₄ electrode exhibits a high specific capacitance of 399.3 mF cm^-2 and good cycling stability. Meanwhile, CN-Fe₃O₄ catalyst exhibits excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities, with overpotentials of 136 and 281 mV at the current density of 10 mA cm^-2, respectively. This work provides a promising approach for the design of high-performance anode materials for supercapacitors and provides profound implications for the development of catalysts with bifunctional catalytic activity.

Molten salt strategy and plasma technology induced MnO2 with oxygen vacancy for high performance Zn-ion batteries

The oxygen vacancy-rich MnO2 was synthesized by the molten salt method and the plasma etching strategy. The amorphous layer increased the active sites and the oxygen vacancies on the surface of MnO2 that promoted the rapid transfer of charges.